Method of boring through hard rock formations

ABSTRACT

The present invention relates to an improved method of boring through hard rock and the like in tunneling and other similar excavating operations. By the present invention at least two shaped charges are placed on the face of the rock to be removed in a manner so that upon detonation of the charges a portion of the rock extending inwardly from the face thereof is softened but not substantially fragmented. After detonation of the charges the resulting softened portion of the rock is removed by mechanical means and upon again reaching hard rock the above-described procedure is repeated.

PIP/5311 United States Patent [1 1 Dorrough et al.

[ METHOD OF BORING THROUGH HARD ROCK FORMATIONS [75] Inventors: Vernon R. Dorrough, Grapevine;

Claude H. Brown, Arlington, both of Tex.

[73] Assignee: Jet Research Center, Inc., Arlington,

Tex.

[22] Filed: Dec. 6, 1973 [2]] Appl. No.: 422,445

[52] U.S. Cl. 299/13, 175/4.6 [51] Int. Cl. E21c 37/00 [58] Field of Search 299/13; l75/4.6

[56] References Cited UNITED STATES PATENTS 1,833,368 11/1931 O'Rourke 299/13 1,872,016 8/1932 Sherwood et al. 299/13 2,616,370 11/1952 Foster 175/46 Feb. 11, 1975 2,869,825 1/1959 Crawford 1. 175/46 3,104,186 9/1963 Lindbergh et al. 299/13 Primary Examiner-James A. Leppink Attorney, Agent, or Firm-Thomas R. Weaver; John H. Tregoning; C. Clark Dougherty, Jr.

[57] ABSTRACT The present invention relates to an improved method of boring through hard rock and the like in tunneling and other similar excavating operations. By the present invention at least two shaped charges are placed on the face of the rock to be removed in a manner so that upon detonation of the charges a portion of the rock extending inwardly from the face thereof is softened but not substantially fragmented. After detonation of the charges the resulting softened portion of the rock is removed by mechanical means and upon again reaching hard rock the above-described procedure is repeated.

11 Claims, 4 Drawing Figures METHOD OF BORING THROUGH HARD ROCK FORMATIONS In forming excavations such as tunnels, boring machines are often utilized which include a rotating cutter head driven by electric or hydraulic motors. The cuttings produced, commonly referredto as muck are picked up by scoopsgenerally mounted onthe periphery of the cutter head, which discharge ontoa belt conveyor extending to the rearward end of the machine.

When such boring machines encounter hard rock formationsor-the like,.the boring operation is considerably slowed down due to the difficulty in removing the rock and the increased wear on the rotating cutter head requiring frequent replacement of the bits or cutters. Heretofore, in order to speed up the boring operation through hard rock and reduce boringmachine wear, drill-and-blast procedures have been used. That is, ex-

plosives are placed in the rock to be removed, after which the area is clearedof operators and equipment and the charges detonated. After detonation of the charges, the mechanical boring equipment is again moved in and drilling and excavation continueduntll hard rock is again encountered at which time the blasting procedure is repeated.

While such heretofore used drill-and-blast procedures generally speed up the boring operation, the

costs involved in carrying out the procedures are high rock is encounteredgenerally includes the steps of backing off the mechanical boring equipment, setting up drilling equipment for drilling a series of blast holes in the rock face, removing the drilling equipment from the tunnel after the holes are drilled, bringing in explosive charges, loading the blast holes with the charges, stemming the blast holes, erecting a blast shield between the rock face and the mechanical boring equipment, clearing the tunnel of personnel, detonating the explosive charges, circulating fresh air through the tunnel to remove fumes produced by the explosion, removing the blast shield from the tunnel, moving the mechanical boring equipment into position for removing the rock fragmented by the explosion, and resuming the boring operation. Due to the inherent delay in each cycle of such drill-and-blast procedures, the rate of advance in boring the tunnel is low. This low rate of advance and requirement for large labor crews to carry out the procedure make thetotal boring costs high.

By the present invention animproved drill-and-blast method of tunneling through hard rock formations and the like is provided wherein the time consuming process of drillingblast holes, loading the blast holes with The improved method of boring through hard rock formations of the present invention basically comprises first placing at least two shaped charges on the face of wardly from the face thereof is softened, that is, the,

hardness of the rock is reduced, but not substantially fragmented. The charges are then detonated and the portion of the rock softened by the detonation is mechanically removed. Upon again reaching hard rock, additional shaped charges are placed on the face thereof and the steps described above repeated.

lnthe accompanying drawings which'form a part of this disclosure:

FIG. 1 illustrates a partially completed tunnel having a conventional tunnel boring machine positioned therein and a plurality of shaped charges placed on the tunnel face,

FIG. 2 is an enlarged view of two of the shaped charges positioned on the face of the tunnel illustrated in FIG. 1,

FIG. 3 is a side sectional view of one charges of FIG. 2, and

FIG. 4 is a plan view of the tunnel face of FIG. 1 illustrating an arrangement of shaped charges which can be used for softening a rock formation.

Referring now to FIG. 1, a partially completed tunnel 10 is illustrated having a conventional boring machine 12 positioned therein. In operation of the boring machine 12, the cutter head 14 thereof, whichincludes a of the shaped plurality of bits, rotates in a vertical plane against the face of' the formation being drilled. The rubble or, as it is referred to in the art, muck produced is picked up by scoops mounted on the periphery of "the cutter-head a variety of boring and excavating machines are com.-

mercially available and the present invention is not limited to theuse of any particular type or design of such apparatus.

When a rock formation is encountered of a hardness such that the boring machine 12 becomes inefficient in lengthening the tunnel 10, the boring operation is stopped and the machine 12 is moved a short distance back from the rock face 18 as shown in FIG. 1; A method commonly used for determining the degree of hardness of rock involves measuring the speed of sound through therock. Conventional testing equipment is available for this purpose, and the harder the rock tested, the higher the velocity of sound throughthe rock. In accordance with the method of the present invention for boring a tunnel or the like through a rock formation, when the rock formation reaches a degree of hardness such that the speed of sound therethrough is in the range of about 7,000 to 10,000 feet per second, the mechanical boring and excavation equipment, which is not substantially functional due to the hardness of the rock, is backed off from the face of the tun nelbAs is well understood by those skilled in the art, the boring equipment can usually only be backed off a short distance from the face of thetunnel due to the construction of a steel or concrete liner for supporting the tunnel walls behind the boring equipment.

Referring still to FIG. 1, after withdrawing the machine 12 from the face 18 of the tunnel l0, a plurality of shaped explosive charges 20 are placed on the face 18 in a manner so that upon detonation of the charges the rock is softened but not fragmented to any great extent. Because the rock is not substantially fragmented when the shaped charges are detonated and because due to the shape of the charges the main force of the TABLE I EXPLOSIVE MATERIALS Symbol Chemical Name Formula RDX Cyclotrimethylenetrinitramine, Hexahydro-l, C l- N 3,5-Trinitro-5-Triazinc, Cyclonite, Hexogen, T4 PETN Pentaerythrite Tetranitrate, Penta, Pentrit, C(CH NO Nitro Pentaerythrite COMP B Cyclotol (RDX +TNT Polyisoluctylene Wax) (55.2/40/l.2/3.6) COMP C Plastite (RDX & Plasticizers Various Percentages) COMP Cl Plastite (RDX & Plasticizer) (883/111) COMP C2 PlHSIllC (RDX & Plasticizer) (78.7/2l.3) COMP C3 Plast te (RDX & Plasticizer) (77/23) COMP C4 Harrisite (RDX & Plasticizer) (91/9) HNS Hexanitrostilbene C H N O DATB Diaminotrinitrobenzene C,,H(NO );,(NH CH6 RDX/Calcium Stearate/Others (97.5/l.5/l.0) TETRYL 2,4,6-Trinitrophenylmethylnitramine, C H,,N,,O

Tetralite, Pyronite, CE

explosion is directed into the rock formation, the boring machine 12 and other equipment positioned behind the rock face are safe from injury or damage. Consequently, in carrying out the method of the present invention, it is not necessary to dismantle portions of the equipment or construct a blast shield in front of the equipment. After detonation of the charges and softening of the rock, i.e., reduction of the speed of sound in the rock to a value preferably below about 7,000 feet per second, the boring machine 12 is moved back into abutment with the face of the rock and the boring operation is resumed. When all of the softened rock has been removed and the degree of hardness once again reaches the point where the speed of sound therethrough is in the range of from about 7,000 to about 10,000 feet per second or more, additional shaped charges are placed on the rock face and the blast-anddrill cycle repeated.

Shaped charges employing the well known lined cavity effect have been used heretofore. Generally, lined cavity shaped charges produce a relatively deep and narrow hole in the target. The shape of the liner and its relationship to the explosive material used produces a successive collapse of the liner upon detonation of the explosives progressing toward and along the axis of the with respect to each other and with respect to the face of the rock to be softened are utilized so that fragmentation of the rock either does not occur or is maintained at a minimum and so that the main force of the explosion is directed into the rock formation.

While a variety of explosive materials can be utilized for forming the shaped charges useful in accordance with the present invention, the explosive material must have a detonating velocity in the range of from about 18,000 to about 28,000 feet per second. Preferably, the explosive material has a detonating velocity from about 20,000 to about 28,000 feet per second, and the most It is to be understood that explosive materials other than those set forth in Table labove can be used. However, the various explosive materials listed in Table l are preferred, and of those, RDX is the most preferred.

The explosive material utilized must be formed into a shaped charge which upon detonation produces an explosion of desired characteristics, i.e., a low mass elongated, unidirectional, deep penetrating jet. Referring to FIGS. 2 and 3, the shaped charges 20 which are particularly suitable for use in accordance with the method of the present invention are illustrated. As best shown in FIG. 3, each of the shaped charges 20 in cludes an outside conical housing or casing 22, explosive material 24 disposed within the casing 22 and a conical liner 26 forming a cavity in the explosive material at the base of the casing 22. In order to prevent the production of flying fragments upon detonation of the shaped charges 20, the casings 22 are preferably formed ofa low density frangible material. Examples of particularly suitable such materials are glass, crushed iron powder, ceramic, and gypsum.

The overall height of explosive material utilized in each of the shaped charges 20 is referred to hereinafter as explosive column height. The explosive column height as well as the specific shape of the explosive material are factors essential in producing the desired results, i.e., the softening ofa rock formation without the substantial fragmentation thereof. The casing 22 can be formed in a variety of shapes such as rectangular or cylindrical, however, the most preferred is a shape substantially in the form of a right circular truncated cone, as shown, having an explosive column height I1. The liner 26 is preferably also formed in the shape of a right circular truncated cone as shown having a vertex angle 0 and a diameter d. The angle 0 of the conical liner 26 must be in the range of from about 45 to about Preferred shaped charges for use in accordance with the present invention include liners having vertex angles in the range of from about 55 to about 65, and the most preferred shaped charge includes a conical liner having a vertex angle in the range of from 57 to 60.

The diameter d of the liner 26 can be in the range of from about 1 inch to about 6 inches. A diameter in the range of from about 1.5 inches to about 4 inches is preferred with the most preferred diameter being in they range of from about 1.7 inches to 3.5 inches.

The ratio of the explosive column height to the diameter (h/d) should be in the range of from about 1:1 to about 3:1. Preferably, h/d is in the range of from about 1.521 to about 2:1 with the most preferred ratio being in the range of from about 1.611 to 1.7:1. The height of the liner (j) can be determined from the following relationship:

J U 1 The explosive column height (h) must be greater than the liner height (i).

As illustrated in FIGS. 1 and 2, the shaped charges 20 are placed on the face of the rock to be softened in a manner such that theaxes of the charges are substantially parallel with each other and are substantially perpendicular to the face of the rock. In addition, each of the shaped charges 20 is positioned to stand off from the rock face 18 a particular distance s. The ratio of the standoff to the diameter of the shaped charges (s/a') is in the range of from about 0.5 to about 3, preferably 0.75 to about 1.5, and most preferably, the standoff distance s is equal to the diameter d.

Still referring to FIG. 2, a preferred technique for placing the shaped charges 20 on the rock face at a desired standoff and spacing is to first attach an arm member 28 to the rock face 18 for each shaped charge to be used. The arm members 28 are conveniently formed from a light, bendable metal strap and are at tached to the rock face 18 by spikes 30. After placement of the arm members 28, the shaped charges 20 are attached thereto such as by conventional clamp members 32 and the desired standoff distance is obtained by bending the arm members 28.

Referring now to FIG. 4, the rock face 18 is illustrated with four shaped charges 20 placed thereon by means of four arm members 28. In order to achieve softening of the rock forming the face 18 preferably without fragmenting the rock upon detonation of the charges 20, the charges 20 must be placed at a particular spacing with respect to each other. That is, the distances (L) between the center lines of the charges 20 must be greater than the diameter (d) of the charges 20 by a factor greater than 7. Preferably, the ratio of the distance between charges to the diameter of the charges used L/d is in the range of from about 7 to about 10. Further, the charges 20 are preferably placed on the rock face 18 in a triangular pattern. That is, the charges should be placed so that straight lines intersecting the center lines of any three adjacent charges define a triangle.

' As illustrated in FIGS. 2 and 4, the charges 20 are connected to a conventional blasting cap 34 by means of lengths of explosive detonating cord 36. Preferably. the charges 20 are connected to the blasting cap 34 in a manner so that substantial simultaneous detonation of the charges 20 occurs after detonation of the blasting cap 34.

As best shown in FIGS. 2 and 3, each of the charges 20 includes a receptacle 38 containing a sensitive explosion initiator material attached to the casing 22 thereof for receiving the explosive detonating cord 36.

The weight of the explosive material utilized in a single shaped charge 20 can vary over a relatively wide range depending upon the number of separate charges to be used in turn is dependent on the weight of target material to be softened. Generally, the weight of explosive material utilized per shaped charge is within the range offrom about 5 grams to about 2,300 grams. Particularly suitable shaped explosive charges for use in accordance with the present invention are those containing explosive material in amounts of grams and one pound (454 grams).

In determining the particular number of shaped charges of known charge weight and design to be used in a particular application, the following relationships are utilized:

L/d 7 D 6P/5 R 3P/5 r 3P/1O W: [(6-06 ")(D)(R Rr r )]p wherein:

W weight of target material to be softened per charge, pounds p density of target material, pounds/foot D depth of disturbance in target material, inches R radius of disturbance caused by single charge at surface of target material, inches r radius of disturbance in target material at D,

inches P maximum penetration'in mild steel test target at standard conditions caused bycharge to be used, inches L distance between center lines of charges, inches d diameter of charges to be used, inches The above relationships are used to determine the number of charges of known charge weight and design to be used, and the spacing between them required to. achieve the desired result, i.e., softening the rock with little or no fragmentation. The value of P must be known and is determined experimentally. The values of P for various sizes of charges are given in Table 11 below.

TABLE II VALUES OF P FOR VARlOUS CHARGES Stand Off Explosive Diameter Vertex Liner Type of Weight of From Face of Penetration in Column of Charge, Angle Height, Explosive Charge, Mild Steel Mild Steel,

Height lnches Inches Material Used Grams Target, lnches lnches (h) U) 1.65 1.63 57 1.5 RDX 80 4.9 9.1 1.65 1.63 57 1.5 RDX 30 0.8 4.85 1.65 1.63 57 1.5 RDX 30 1.6 4.83 1.65 1.63 57 1.5 RDX 30 2.4 6.15 -63. N 1- RDX 3 3-.

TABLE 11 Continued VALUES OF P FOR VARIOUS CHARGES Stand Off Explosive Diameter Vertex Liner Type of Weight of From Face of Penetration in Column of Charge, Angle Height, Explosive Charge, Mild Steel Mild Steel,

Height lnches Inches Material Used Grams Target. lnches Inches U) 1.65 1.63 57 1.5 RDX 20 0.8 4.28 1.65 1.63 57 1.5 RDX 20 1.6 5.35

3- wide X 3" long X 1" thick mild steel plates stacked one on top of the other and clarnped together with test charge positioned above top plate so that force of explosion directed substantially normal to face of top plate. 2" wide X 2" long X 2" thick steel plates used.

As will be understood, each different size and/or shape of shaped charge has a different penetration in a mild steel test target (P) and the data presented in Table II represents only a few of the many sizes and shapes of charges that can be used.

In order to present a clear understanding of how the relationships given above are utilized, let it be assumed that the penetration (P) in a mild steel test target achieved by an 80 gram RDX shaped charge of the present invention is 15 inches, the charge has a diame ter (d) of 1.692 inches and an explosive column height (/1) of 2.9 inches, and the rock to be softened has a density (p) of 150 pounds/feet", then:

D 6/5 (15) 18 inches R 3/5 (15) 9 inches r 3/10 (15) 4.5 inches W= (6.06 X l0)(l8)(8l 40.5 20.25)(l50) 231.9 pounds of rock If such charges are used, the spacing is:

L 7 X L692 L 11.8 inches Thus 3 such charges at a spacing of about l2 inches between center lines will soften approximately 695.7 pounds of rock.

In order to more clearly illustrate the present invention, the following examples are given:

EXAMPLE 1 Five 80 gram RDX shaped charges having the following dimensions are placed on a granite rock face:

d== 1.692 inches h 2.9 inches The charges are positioned at a standoff (s) of 2.5 inches and in a triangular pattern wherein the distance (L) between the center lines of each two charges is 12 inches (L/d 7.1). The charges are detonated simultaneously with the result that cavities are formed in the face of the rock at each charge location having an average depth (D) of 6 inches, a surface radius (R) of about 3 inches, and a radius (r) at the bottom of about 1.5 inches. The face of the rock also contains visible fractures running between the cavities.

The average penetration (P) in mild steel caused by a single charge of the size and at the standoff mentioned above is about inches.

EXAMPLE 2 Three 1 pound RDX shaped charges having the following dimensions are placed on a granite rock face:

d 3.5 inches /1 5.4 inches The charges are positioned at a standoff (s) of 8 inches in a triangular pattern wherein the distance (L) between the center lines of each two of the charges is 30 inches (L/d 8.6). The charges are detonated simultaneously resulting in the formation of cavities in the rock at the area of placement of each of the charges, the cavities having an average depth (D) of 17 inches, an average surface radius (R) of 8.5 and an average radius (r) of 4.3 inches.

In order to verify that the detonation of the shaped charges softened the rock, prior to the detonation a 1 /8 inch diameter hole is drilled in the rock using a conventional rock drill to a depth of 32 inches in 8 minutes. After detonation of the shaped charges, the same rock drill is used in the same manner to drill another 1 /8 inch hole and this time a depth of 42 inches is reached in only 3 minutes.

The average penetration (P) in mild steel brought about by a single charge of the size and at the standoff mentioned above is about 14 inches.

The present invention therefore is well adapted to carry out and attain the benefits and advantages mentioned as well as those inherent therein. While presently preferred embodiments of the invention have been described for the purpose of this disclosure, numerous changes can be made which will readily suggest themselves to those skilled in the art and which are encompassed within the invention as defined by the appended claims.

What is claimed is:

1. A method of excavating rock comprising the steps of:

a. placing at least two shaped charges on the face of the rock to be excavated so that the spacing between the center lines of said charges is greater than the diameter of said charges by a factor greater than 7 and so that upon detonation the energy from said charges is directed inwardly from the face of said rock whereby a portion of said rock is softened but not substantially fragmented;

b. detonating said charges; and

c. mechanically removing the portion of said rock softened by the detonation of said charges.

2. The method of claim 1 wherein each of said shaped charges includes an explosive material characterized by a detonating velocity in the range of from about 18,000 to about 28,000 feet per second.

3. The method of claim 2 wherein each of said charges is formed substantially in the shape of a truncated cone, the base of which includes an inner lined conical cavity.

4. The method of claim 3 wherein said conical cavity has a vertex angle in the range of from about 45 to about 5. The method of claim 4 wherein the base diameter of each said conical cavity of each of said shaped charges is in the range of from about 1 inch to about 6 inches.

6. The method of claim wherein the ratio of the height of each of said shaped charges to the base diameter thereof is in the range of from about 1:1 to about 3:1.

7. The method of claim 6 wherein each of said charges is positioned with the axis thereof substantially perpendicular to the face of said rock andso that the base thereof stands off from the face of said rock a distance greater than the diameter of said charge by a factor in the range of from about 0.75 to about 3.

8. A method of boring through rock comprising the steps of:

a. attaching at least two shaped charges each formed substantially in the shape of a right circular truncated cone and including an inner lined conical cavity at the base thereof on the face of the rock to be removed, the spacing between the center lines of said charges being greater than the diameter thereof by a factor in the range of from about 7 to about 10 and the standoff of said charges from the face of said rock being a distance greater than the diameter of said charges by a factor in the range of from about 0.75 to about 3 so that upon detonation of said charges energy is directed into the rock and a portion of the rock extending inwardly from the face thereof is softened but not fragmented;

b. detonating said charges;

c. mechanically removing the portion of said rock softened by the detonation of said charges; and

d. repeating steps (a) through (c).

9. The method of claim 8 wherein each of said shaped charges includes an explosive material characterized by a detonating velocity in the range of from about 18,000 to about 28,000 feet per second.

10. The method of claim 9 wherein the diameter of each said conical cavity of each of said shaped charge is in the range of from about 1 inch to about 6 inches and the ratio of the height of said charge to the diameter of the base thereofis in the range of from about 1:] to about 3:l.

ll. The method olclaim 10 wherein the vertex angle of the inner conical cavity of each of said shaped charges is in the range of from about 45 to about 70. 

1. A method of excavating rock comprising the steps of: a. placing at least two shaped charges on the face of the rock to be excavated so that the spacing between the center lines of said charges is greater than the diameter of said charges by a factor greater than 7 and so that upon detonation the energy from said charges is directed inwardly from the face of said rock whereby a portion of said rock is softened but not substantially fragmented; b. detonating said charges; and c. mechanically removing the portion of said rock softened by the detonation of said charges.
 2. The method of claim 1 wherein each of said shaped charges includes an explosive material characterized by a detonating velocity in the range of from about 18,000 to about 28,000 feet per second.
 3. The method of claim 2 wherein each of said charges is formed substantially in the shape of a truncated cone, the base of which includes an inner lined conical cavity.
 4. The method of claim 3 wherein said conical cavity has a vertex angle in the range of from about 45* to about 70*.
 5. The method of claim 4 wherein the base diameter of each said conical cavity of each of said shaped charges is in the range of from about 1 inch to about 6 inches.
 6. The method of claim 5 wherein the ratio of the height of each of said shaped charges to the base diameter thereof is in the range of from about 1:1 to about 3:1.
 7. The method of claim 6 wherein each of said charges is positioned with the axis thereof substantially perpendicular to the face of said rock and so that the base thereof stands off from the face of said rock a distance greater than the diameter of said charge by a factor in the range of from about 0.75 to about
 3. 8. A method of boring through rock comprising the steps of: a. attaching at least two shaped charges each formed substantially in the shape of a right circular truncated cone and including an inner lined conical cavity at the base thereof on the face of the rock to be removed, the spacing between the center lines of said charges being greater than the diameter thereof by a factor in the range of from about 7 to about 10 and the standoff of said charges from the face of said rock being a distance greater than the diameter of said charges by a factor in the range of from about 0.75 to about 3 so that upon detonation of said charges energy is directed into The rock and a portion of the rock extending inwardly from the face thereof is softened but not fragmented; b. detonating said charges; c. mechanically removing the portion of said rock softened by the detonation of said charges; and d. repeating steps (a) through (c).
 9. The method of claim 8 wherein each of said shaped charges includes an explosive material characterized by a detonating velocity in the range of from about 18,000 to about 28,000 feet per second.
 10. The method of claim 9 wherein the diameter of each said conical cavity of each of said shaped charge is in the range of from about 1 inch to about 6 inches and the ratio of the height of said charge to the diameter of the base thereof is in the range of from about 1:1 to about 3:1.
 11. The method of claim 10 wherein the vertex angle of the inner conical cavity of each of said shaped charges is in the range of from about 45* to about 70*. 